day 15 part 1

AdventOfCode/Day15.cs

@@ -0,0 +1,120 @@
+
+namespace AdventOfCode;
+
+public class Day15 : BaseDay
+{
+    private readonly char[][] _map;
+    private readonly List<char> _moves = new List<char>();
+    private Position _robot;
+
+    public Day15()
+    { 
+        string[] lines = File.ReadAllLines(InputFilePath);
+
+        int width = lines[0].Length;
+        int height = lines.Count(l => l.StartsWith("#"));
+
+        _map = new char[height][];
+        for (int i = 0; i < height; ++i)
+        {
+            _map[i] = lines[i].ToCharArray();
+
+            int j = lines[i].IndexOf('@');
+            if (j >= 0)
+            {
+                _robot = new Position(i, j);
+            }
+        }
+
+        foreach (var line in lines.Skip(height + 1))
+        {
+            _moves.AddRange(line.ToList());
+        }
+    }
+
+    public override ValueTask<string> Solve_1()
+    {
+        foreach (char move in _moves)
+        {
+            Move(move);
+        }
+
+        int gps = GetGPS();
+
+        return new(gps.ToString());
+    }
+
+    public override ValueTask<string> Solve_2()
+    {
+        return new("");
+    }
+
+    private void Move(char move)
+    {
+        Position next = GetNext(move, _robot);
+
+        Position firstNext = next;
+        bool movesBoxes = false;
+
+        while (true)
+        {
+            char nextChar = _map[next.I][next.J];
+            if (nextChar == '#')
+            {
+                return; // wall = do nothing
+            }
+            if (nextChar == '.')
+            {
+                if (movesBoxes)
+                {
+                    _map[next.I][next.J] = 'O';
+                }
+                _map[firstNext.I][firstNext.J] = '@';
+                _map[_robot.I][_robot.J] = '.';
+                _robot = firstNext;
+                return;
+            }
+            if (nextChar == 'O')
+            {
+                next = GetNext(move, next);
+                movesBoxes = true;
+            }
+        }
+    }
+
+    private Position GetNext(char move, Position from)
+    {
+        switch (move)
+        {
+            case '^':
+                return new Position(from.I - 1, from.J);
+            case 'v':
+                return new Position(from.I + 1, from.J);
+            case '>':
+                return new Position(from.I, from.J + 1);
+            case '<':
+                return new Position(from.I, from.J - 1);
+            default:
+                throw new NotImplementedException();
+        }
+    }
+
+    private int GetGPS()
+    {
+        int result = 0;
+        for (int i = 0; i < _map.Length; ++i)
+        {
+            for (int j = 0; j < _map[i].Length; ++j)
+            {
+                if (_map[i][j] == 'O')
+                {
+                    result += 100 * i + j;
+                }
+            }
+        }
+
+        return result;
+    }
+
+    private record Position(int I, int J);
+}